Do liquids with a higher density always have a higher viscosity?

Answer 1

Just reacting to this might lead someone to say yes to the question. But no, liquids with a higher density don't always have a higher viscosity. Different liquids have mechanical properties based on their composition and other variables. Temperature is one. A temperature change of 5 degrees can double the viscosity of some things, and yet others will maintain a fairly constant viscosity over a broad temperature range. There can be a lot of range in material properties. The general rule (though not a hard and fast one) is that the larger the molecules of a substance, the greater its viscosity. Compare black strap molasses to the amazing metal Mercury. At room temperatue, the molasses takes quite a while to come out of the bottle. Mercury will come out of a bottle about as fast as water would. The mercury has a dynamic viscosity of about 1.5 cP, while that of water is a tiny bit over 1 cP. Olive oil rates about 85 cP, and molasses goes up way beyond that. Let's take a little trip through time and space. Remember those things that played vinyl records? Turntables? They'd gone "out of style" a while back - 'til the DJ's brought 'em back! Anyway, remember the tiny needle that tracked the groove in the record? That's the stylus. And the cartridge (or "cart") is the thing that the stylus fit into. The cart was put onto the head shell, and the headshell onto the end of what was called the tonearm. And the tonearm had a little lever that lifted the whole arm up. Are we good? Now let's look at the action of the arm. If we put a record on the turntable, unlocked the tonearm, and then lifted it with the lift lever (or cueing lever), we'd then move the tonearm over to the place (the track) where we wanted to put the stylus. This is how we cue the tonearm. We'd cue the tonearm, and them push the lever down to drop the arm. But the arm wouldn't drop. I wasn't supposed to. The arm would actually "coast" or "glide" down in slow motion. If you have a chance to see this in action, watch it. The reason for the "slow motion" descent was that there was some silicone tonearm damping fluid in the little cylinder that had to collapse for the tone arm to go down. And if you had a little bottle of this silicone tone arm damping fluid, you could invert it, go warm your coffee in the microwave oven and return to find it hadn't moved very much at all. It would be hard to detect its motion. Its viscosity is very, very high. And it's about as dense as vegetable oil. Who knew, huh? And let's not even get started about glass.